Buckthorn

Buckthorn, the English name for the species of Rhamnus, the typical genus of the order Rhamnaceae, which are mostly spinous shrubs, and two of which, R. catharticus and R. frangula, are natives of Britain. They are mostly natives of the northern temperate zone, and have simple, petiolate, glabrous, pinnately-veined leaves; axillary clusters of greenish, often unisexual flowers; and a drupaceous fruit containing two, three or four one-seeded stones or pyrenees. R. catharticus, the purging buckthorn, has its branches terminated by spines, and its flowers tetramerous. Its bark and fruit are violently purgative. R. frangula has no spines and pentamerous flowers, and, as its foliage resembles that of the alder, it is called alder buckthorn or berry-bearing alder. Its wood, known as "dog-wood," is in request for gunpowder charcoal. Yellow or Persian berries are the unripe fruits of R. infectorius, imported from Smyrna; Avignon berries, the same species from South France, both being used in calico printing. Chinese green indigo or Lo-kao, used in dyeing Lyons silk, is prepared from the bark of R. utilis and R. chlorophorus; and the safer cathartic known as Cascara Sagrada ("sacred bark") from that of R. Purshianus.